The present invention relates to both the field of education and demonstration, and the field of measuring and testing. More specifically, it relates to instrumented educational structural models; plug-in motion-sensing accelerometers; and fluidic structural strain gauges. Operation involves testing the behavior and monitoring the health of familiar structural models: a swing, a beam, and a free-fall rig, instrumented with novel motion and strain sensors.
Almost since the dawn of human thought, physical models have been created and employed to help explain, demonstrate, teach, and explore the wonders of nature and creation. Today, in our modern, computerized, information age, such models proliferate. Physical, mental, pictorial, graphical, symbolic, verbal, and virtual, models play a vital role in our highly industrialized society.
With the relatively recent advent of computers, and the development of a multitude of electronic sensors, instrumented structural models of such things as building, bridges, bones, machines, cars, and satellites now occupy much space and attract attention in our government, industrial and educational laboratories. A legion of busy scientists and technologists laboriously test and modify the behavior, and monitor the health of these structural models. A typical human task today might involve creating, testing, modeling and modifying the behavior of a structure to improve how it functions, feels, looks, sounds, interacts, or copes.
Of course, this enterprising situation also creates a need for educational and demonstration models to help educate and train students and workers, as well as the general public. To do a better job, workers need to further develop their natural testing talents and communicating skills, as well as to learn more about the automatic, interactive nature and behavior of things. Even ancient biblical wisdom encourages them to test all things, and retain what is good.
Just to reasonably cope in our modern technical society, people in general need to be more aware of important scientific endeavors, such as the space station, Freedom, which has undergone extensive behavior testing in model form, and to become more familiar with scientific testing methods and the basic universal technology involved.
In structural dynamics laboratories at major universities, sophisticated, instrumented, educational models now help students to naturally and interactively learn in a fun way by doing, testing, relating and repeating. Such models often employ various types of commercial sensors, such as capacitance, resistance, inductance and piezo-electric, to measure motion, force, pressure, sound, and other physical variables. But several perplexing problems still plague these structural models and the sensors involved.
Employing industrial components and designs, present educational structural models are usually quite expensive, difficult to adjust and operate, and inconvenient to instrument with sensors.
Older educational models fail to promote and demonstrate modern, universal, structural technology and terminology. For example, today sensors are structures, not mystical devices. Like humans, sensors employ structures and the natural energetic way that structures interact to sense and communicate information. And all of the technology and terminology taught in the university courses applies to the sensor structure as well as to that of the test object.
Expensive commercial and industrial sensors are usually not suitable for educational applications because of difficulties installing and removing them, especially on test objects requiring several sensors or an array of sensors. Bending or twisting the sensors instead of removing them in a prescribed linear way often damages delicate electrical pin connections or electrical cables.
Installing commercial motion sensors has always been an arduous, time consuming, precision task. Much time, money and research effort has been invested in developing improved mounting means, including stud, bolt, clamp, pad, adhesive, tape, wax, and magnets. Popular stud mounting, which mechanically clamps imperfect mating surfaces together into intimate contact has proven to be the best behaving method, although not always convenient or practical. Any interface irregularities or added interface structures modify the motion of the sensor, causing errors at higher frequencies of interest.
Highly perfected microphone technology offers a promising solution to low-cost, educational motion and strain sensors, especially in applications requiring very high sensitivity. But unsuccessful attempts over the past two decades to modify and convert low-cost, electret microphone structures into motion-sensing accelerometers have failed because of difficulty in attaching a small seismic mass to the flimsy diaphragm, usually made of an extremely thin, metalized plastic film. Any slight inadvertent force during assembly stretches and relaxes the taut diaphragm, rendering it useless for accelerometers.
Accordingly, many of the above problems and difficulties are obviated by the present invention, which provides an educational structural model incorporating an easily adjustable, pendulous swing; an impact-actuated, free-fall test rig; and a strain-gauged cantilever beam; all instrumented with a low-cost, easy-to-install, electrostatic motion-sensor assembly, and all partially and economically made of a stiff, hard, compressible, elastic material.
In the free-fall rig, a falling actuator mass impacts a junction block to relax a flexible filament suspension line, which allows the instrumented test-object mass to fall freely for a brief interval of time, confirming Newton""s famous Law of Motion, force equals mass multiplied by acceleration, or F=ma.
Somewhat surprisingly, in the adjustable swing assembly, sensor signals faithfully track the arcing motion of a glider-type swing, but not that of simple swing. This strange phenomena demonstrates what happens or doesn""t happen when structures do not energetically interact. The compressible material in the swinging mass grips a one-piece, continuous loop, flexible, filament suspension line; holding the transformable swing in adjustable alignment with the frame of the educational structural model.
In the cantilever beam model, compression and expansion of a fluidic strain sensor converts the surface distortion of a vibrating beam into an oscillating, decaying signal for visual display on a monitoring instrument.
The low-cost, accelerating motion sensor involved conveniently plugs into or onto the test object or a mounting pad accessory, and intimately clamps imperfect interface mounting surfaces together with a residual compressive force, similar to a popular stud mount. Pressing and slightly twisting the sensor into a mounting hole compresses the elastic material in the vicinity of the interface, grips the test object to retain some of the compressive stress, and deflects enough to conform to irregularities in the mounting surface of the test object. After installing the compressible sensor with a slight twisting motion, it""s quite difficult to pull it straight off.
Natural damping inherent in the hard-rubber body material reduces the tendency for sensitivity of the motion sensor to increase at higher frequencies. An external O-ring clamping the electrical cable to the body acts as a strain relief against any inadvertent forces tugging on the cable,
Therefore, the primary object of this invention is to provide an instrumented, adjustable, educational, structural model for calibrating accelerometers; for demonstrating behavior-testing and health-monitoring of machinery technology; and for exploring the radiant, vibrant, automatic, communicative nature and behavior of energetically interacting things.
Another object of this invention is to physically demonstrate with familiar objects how through energetic interactions, which involve a transfer of energy, things function to transfer forces of nature into motion; how the behavior of a structure depends upon the way it transfers, converts, stores, or dissipates the energy involved; and how energetically interacting structures can be employed to sense and communicate information.
Still another object of this invention is to provide a low-cost motion sensor that quickly and conveniently installs by plugging into a hole or onto a post on a test object, mounting pad, or calibrator, whose motion is to be measured.
Still another object of the present invention is to provide a rugged motion sensor that can withstand student abuse, and will not be damaged by pulling, twisting or bending to remove it from the test object.
Still another object of the present invention is to provide a sealed motion sensor not appreciably affected by environmental moisture or humidity.
Still another object of the present invention is to convert low-cost, mass-produced, popular microphone cartridges into practical motion-sensing accelerometers by attaching a seismic mass to the diaphragm to enhance the inherent acceleration sensitivity.
Still another object of this invention is to provide a compatible, convenient, fluidic strain sensor that mechanically or adhesively installs on a surface of a test object.